Device for cutting a paper web in the transverse direction

ABSTRACT

A device for cutting a paper web in a transverse direction includes a first continuously driven conveyor for moving the paper web through the device, a loop forming station, a cutting device, a clamping device for temporarily retaining the paper web, and a second conveyor for moving the paper web further after it is stored. The second conveyor includes a continuously driven transport roller and pressure rollers that are intermittently pressed onto the transport roller. The clamping device and the lifting device are driven in step with the cutting device so that the paper web is retained by the clamping device and the pressure rollers are lifted from the transport roller while the paper web is cut. The lifting device controls and lifts the pressure rollers of the second conveyor from the transport roller shortly before the paper web is stretched when the loop is undone.

The invention relates to a device for cutting a paper web in atransverse direction, comprising a continuously driven first conveyor,by means of which the paper web is moved at a constant first conveyingspeed into the device and is there stored in the form of a loop duringthe cutting operation, comprising a stationarily arranged cuttingdevice, comprising a clamping device for the intermittent clamping ofthe paper web, and comprising a second conveyor to move the paper webafter its storage at a second conveying speed increased in comparison tothe first conveying speed, consisting of a continuously driven transportroller and several pressure rollers which can be intermittently pressedon the transport roller with the interpositioning of the paper web bymeans of a lifting device, whereby the clamping device and the liftingdevice can be driven in step with the cutting device in such a mannerthat for the duration of the cutting operation, the paper web is clampedby the clamping device, and the pressure rollers are lifted off from thetransport roller.

BACKGROUND OF THE INVENTION

The second conveyor is, in a conventional device for the transversecutting of a paper web of this type (DE 31 31 101 A1), arranged in afeed direction of the paper web in front of the clamping device and thelatter is placed directly in front of the cutting device. A joint crankdrive is provided to operate the clamping device, the cutting device andthe lifting device, which joint crank drive coordinates through threeconnecting rods the movements of the aforementioned devices in such amanner that for the duration of the cutting operation the paper web isclamped by the clamping device and the pressure rollers are lifted offfrom the transport roller. Since during the clamping of the paper webthe first conveyor continuously runs and the second conveyor is inactivebecause of the lifted-off pressure rollers, a loop is formed in the areain front of the second conveyor. As soon as the cutting operation hasended, the pressure rollers are again pressed on the transport roller ofthe second conveyor and the paper web is moved on by said secondconveyor at a conveying speed, which is increased relative to the firstconveying speed, which first causes the loop to be undone and the paperweb to be tightened. The paper web is subsequently moved on by the firstconveyor and the second conveyor. The pressure rollers of the secondconveyor are pressed by spring force on the transport roller, wherebythis spring force is adjusted so weak that, with the paper web beingtightened, slip occurs between the transport roller rotating at a highspeed and the paper web. The conveying speed of the web is determinedexclusively by the conveying speed of the first conveyor. In order forthe mentioned slip between the transport roller of the second conveyorand the paper web to be able to occur, the second transport roller isdesigned as a metal roller. The maximum possible pulling force is herebylimited on the one hand in such a manner that no pressure pointswhatsoever may show in the paper web when the mentioned slip occurs, andon the other hand the paper web at the moment of the tightening of thesame, when the loop has just been undone, may not tear. The secondconveyor has thus a relatively small pulling force and therefore cannotsufficiently quickly accelerate the paper web from standstill, after ithas been released from the clamping device, thus causing the cuttingperformance of this known device to be very limited. Furthermore, therealso exists the danger of a paper jam. Namely, in order to achieve an ashigh as possible cutting performance, the pressure rollers of the secondconveyor must, after the cutting operation has ended, be pressed asquickly as possible again on the transport roller. When at this time theclamping jaws of the clamping device are not yet completely opened,there exists the danger that the paper web gets caught on the partiallyopen clamping jaws and a paper jam occurs. The pressure rollers cantherefore only be pressed on the transport roller when the completeopening of the clamping device has been secured. This also results inlimiting the cutting performance.

Another conventional device for the transverse cutting of a paper web(DE 196 24 277) has a design similar to the aforedescribed device, withthe difference that the second conveyor is arranged between the clampingdevice and the cutting device, and that this second conveyor lacks alifting device for lifting off the pressure rollers. The pressurerollers are in this conventional device continuously pressed by springforce on the continuously driven transport roller of the secondconveyor. Since same is arranged in paper running direction behind theclamping device, however, the paper web is clamped by the clampingdevice during the cutting operation, a slip between the second conveyorand the paper web must be possible during the cutting operation. Inorder to accomplish this, the transport roller of the second conveyor isdesigned as a metal roller and the spring force acting on the pressurerollers is adjusted relatively low. The maximum possible pulling forceof the second conveyor is here also limited in such a manner that nopressure points whatsoever may show in the paper web when the mentionedslip occurs and the paper web, at the moment of a tightening of thesame, when the loop has just been undone, may not tear. Thus the secondconveyor has here also a relatively small pulling force and cantherefore not sufficiently quickly accelerate the paper web fromstandstill, after it has been released from the clamping device. Thecutting performance also of this conventional device is limited in thismanner at a form length of approximately 9 cm to 50,000 cuts per hour.

The basic purpose of the invention is therefore to provide a device forthe transverse cutting of a paper web of the above-identified type,which most of all enables a significant increase in the cuttingperformance.

SUMMARY OF THE INVENTION

This is attained according to the invention in such a manner that thesecond conveyor is arranged between the clamping device and the cuttingdevice, that the transport roller of the second conveyor has a surfacecoating with an as large as possible coefficient of friction relative tothe paper web, and that the lifting device is designed such or can becontrolled such that the pressure rollers are lifted off from thetransport roller just prior to the paper web being tightened through ataking up of the loop.

The pressure rollers of the second conveyor can in this new device forthe transverse cutting of a paper web be pressed immediately followingthe end of the cutting operation again on the transport roller of thesecond conveyor. As soon as this has taken place, the initially restingpaper web is much accelerated by the transport roller. This highacceleration is possible because the surface coating of the transportroller has a high coefficient of friction relative to the paper web andcan therefore transmit a high pulling force to same. The paper web canbe accelerated already at a time, at which the clamping device is onlypartially open since the second conveyor is arranged behind the clampingdevice and therefore pulls the paper web through the clamping device.The danger of a paper jam at the clamping device is thus eliminated. Itis also important that the pressure rollers are again lifted off fromthe transport roller by the lifting device shortly before the paper loopis undone and the paper web is tightened. Otherwise the paper web wouldnamely tear due to the high acceleration of the paper web and the highpulling force of the transport roller. As a whole the time needed for anundoing of the loop is significantly shortened by the high accelerationof the paper web, which in particular in the case of short form lengthsresults in a significant increase of the cutting performance. Thus itis, for example, possible at a form length of 10 cm to achieve a cuttingperformance of up to 100,000 cuts per hour or more than 27 cuts persecond. This means that within a time period of only 0.036 seconds thepaper web is accelerated from standstill after the end of a cuttingoperation, is moved 10 cm by the second conveyor, is clamped by means ofa clamping device, and is cut by the cutting device. At a form length ofapproximately 30 cm, the new device makes it still possible to reach acutting performance of up to approximately 36,000 cuts per hour.

BRIEF DESCRIPTION OF THE DRAWING

The drawing schematically illustrates one embodiment of the papercutting device.

DETAILED DESCRIPTION OF THE INVENTION

The paper web P is continuously fed to the device for the transversecutting by means of a first conveyor 1 consisting of a driven transportroller 1 a and a pressure roller 1 b. The transport roller 1 a iscontinuously driven with a first peripheral speed V1 and gives the paperweb a conveying speed V1, which corresponds, for example, to thedelivery speed of a not illustrated laser printer connected in frontthereof. The first conveyor can also be a so called tractor consistingof two conveyor belts arranged parallel to one another and engaging withtheir points the perforations in the longitudinal edges of the paperweb. A loop-forming station 3 follows the first conveyor 1, the functionof which will be discussed in greater detail later on in connection withthe description of the operation of the device. The loop-forming station3 is followed by a clamping device 4, consisting of at least onestationary clamping jaw 4 a and a movable clamping jaw 4 b. A secondconveyor 6 is provided between the clamping device 4 and a cuttingdevice 5. The cutting device 5 is preferably a cutting device with arotating knife 5 a, which cooperates with a stationary knife 5 b.However, it is also possible to provide a cutting device with one up anddown movable knife and one stationary knife.

The second conveyor device 6 consists of a continuously driven transportroller 6 a and several pressure rollers 6 b, which can be pressed on thetransport roller with the interpositioning of the paper web P. Thepressure rollers 6 b are arranged spaced apart on a common axle 7. Thetransport roller 6 a has a surface coating or a layer 8, which has an aslarge as possible coefficient of friction relative to the paper web P.The surface coating 8 consists preferably of a rubber-elastic material,in particular of polyurethane elastomer on the basis ofnaphthalin-1,5-diyldiisocyanate (known under the registered TrademarkVulkollan).

The pressure rollers 6 b can according to the invention be pressedintermittently on the transport roller 6 a with the interpositioning ofthe paper web P. A lifting device 9 is provided for this purpose. Sameconsists of a rotatable cam plate 10 and a rocker arm 11, on the freeend of which is arranged the axle 7. The rocker arm 11 is supportedthrough a support roller 12 on the cam plate 10. A spring 13 assuresthat the support roller 12 is always held on the cam plate 10. Themovable clamping jaw 4 b of the clamping device 4 is driven in a similarmanner through a cam plate 14, a rocker arm 15 and a support roller 16.

The cam plates 10 and 14 and the rotating cutting knives 5 a are drivenby a common motor 17, which causes the drive of the lifting device 9 andof the clamping device 4 to occur in step with the cutting device 5.

A third conveyor 18 is advantageously additionally provided between theclamping device 4 and the cutting device 5, which conveyor 18 isadvantageously arranged adjacent to the clamping device 4, whereas thesecond conveyor 6 is provided adjacent to the cutting device 5. Thethird conveyor 18 consists of a continuously driven transport roller 18a and several pressure rollers 18 b pressed on the transport rollers bysprings. The transport roller 18 a has a metal surface. The bearingpressure, with which the pressure rollers 18 b are pressed on thetransport roller 18 a with the interpositioning of the paper web P, ischosen in such a manner that the transport roller 18 a can continue torotate even when the paper web is clamped in without leaving pressurepoints in the paper web.

The two transport rollers 6 a and 18 a are driven continuously with aperipheral speed V2, which is higher than the peripheral speed V1 of thefirst conveyor 1.

A fourth conveyor 19, also consisting of a continuously driven transportroller 19 a and several pressure rollers 19 b, which can be resilientlypressed on the roller 19 a with the interpositioning of the paper web P,is provided behind the cutting device 5. The peripheral speed V2 of thetransport roller 19 a corresponds with the peripheral speed of thetransport rollers 6 a and 18 a.

The so far described device operates as follows:

The paper web P is moved at a constant speed by the first conveyor intothe device of the invention for the transverse cutting. The paper web isthen cyclically clamped by the clamping device 4 while the cuttingdevice 5 carries out the cutting operation. While the paper web isclamped by the clamping device 4, the paper web P is continuously movedon by the first conveyor 1, and the amount of paper moved thereby isstored in the form of a loop 20 in the loop forming station 3. While thepaper web is clamped by the clamping device 4, the transport roller 18 aof the third conveyor 18 rotates while slidingly engaging the paper web,whereby, however, the pressure rollers 6 b of the second conveyor 6 arelifted off from the transport roller 6 a, and the transport roller 6 adoes not apply any transporting action to the paper web. The paper cutoff by the cutting device 5 is moved on by the fourth conveyor 19. Afterthe cutting operation has been carried out, the clamping device 4 isreleased by the cam plate 14 and the pressure rollers 6 b are at thesame time pressed on the transport roller 6 a by the cam plate 10. Dueto the high coefficient of friction of the surface coating 8 thetransport roller 6 a applies a high pulling force to the paper web P andspeeds the paper web up in the shortest time to an increased conveyingspeed, which corresponds with the peripheral speed V2 of the transportroller 6 a and also of the transport roller 18. Since the peripheralspeed V2 is greater than the conveying speed V1 of the first conveyor 1the paper loop 20 formed during the clamping of the paper web is undone.Just before the paper loop is undone and the paper web is tightened, thepressure rollers 6 b must again be lifted from the transport roller 6 asince the paper web would otherwise tear. The on-time lifting of thepressure rollers 6 b is done by a suitable design of the cam plate 10.The paper web is, with the pressure rollers 6 b being lifted, moved onby the third conveyor 18 and in the case of larger form lengths also bythe fourth conveyor 19 until the predetermined form length has beenreached. The paper web is subsequently again clamped by means of theclamping device 4 and the cutting is done by means of cutting device 5.Through the intermittently acting transport roller 6 a with a surfacecoating 8 with a high coefficient of friction relative to the paper web,the paper web is accelerated within the shortest time, thussignificantly shortening the duration of a taking up of the loop 20, inparticular in the case of short form lengths. This results in asignificant increase in the performance of the entire device.

The cam plates 10, 14 illustrated in the drawing can also have anoutwardly limited control cam in the form of a groove, into which therollers 12 or 16 engage from the side. An automatic control of therollers 12 or 16 upwardly and downwardly is achieved in this manner andthe spring 13 can be eliminated.

What is claimed is:
 1. A device for the transverse cutting of a paperweb, comprising: a first continuously driven conveyor for moving thepaper web at a first constant conveying speed into the device; aloop-forming station in the form of a loop for storing the paper webduring a cutting operation; a clamping device arranged in apaper-running direction from the loop-forming station for intermittentclamping of the paper web; a second conveyor provided in thepaper-running direction from the clamping device to move the paper webon after being stored by the loop-forming station at a second conveyingspeed greater than the first conveying speed, the second conveyorcomprising a continuously driven transport roller and several pressurerollers for intermittently pressing on said transport roller; a liftingdevice for interpositioning of the paper web by lifting the pressurerollers; and a cutting device stationarily arranged in the paper-runningdirection from the second conveyor, wherein the clamping device and thelifting device are driven in step with the cutting device so that, forthe duration of the cutting operation, the paper web is closed by theclamping device and the pressure rollers are lifted from the transportroller, wherein the transport roller of the second conveyor includes asurface coating of a rubber-elastic material, and the lifting device iscontrolled so that the pressure rollers are lifted off from thetransport roller before the loop is undone and the paper web istightened.
 2. The device according to claim 1, wherein the surfacecoating consists of polyurethane-elastomer on the basis ofnaphthalin-1,5-diyldiisocynate.
 3. The device according to claim 1,wherein the lifting device includes a cam gear.
 4. The device accordingto claim 1, wherein a third conveyor is arranged between the clampingdevice and the cutting device, the third conveyor comprising acontinuously driven transport roller and several pressure rollers forresilient pressing on said transport roller, so that said transportroller is driven at the same peripheral speed as the transport roller ofthe second conveyor.
 5. The device according to claim 4, wherein thesecond conveyor is arranged adjacent to the cutting device and the thirdconveyor is arranged adjacent to the clamping device.
 6. The deviceaccording to claim 4, wherein the transport roller of the third conveyorincludes a metal surface.
 7. A device for transverse cutting of a webcomprising: a first conveyor for moving the web along a path of travelat a first conveying speed; a loop-forming station arranged downstreamalong the path of travel of the web from said first conveyor for storingthe web as a loop during a clamping and cutting operation; a clampingdevice arranged downstream from said loop-forming station along the pathof travel of the web for periodic clamping of the web; a second conveyorprovided downstream from said clamping device to move the web, afterbeing stored by said loop-forming station, at a second conveying speedwhich is greater than the first speed, said second conveyor comprising acontinuously driven transport roller and pressure rollers; a liftingdevice for periodically pressing said pressure rollers on said transportroller of said second conveyor to enable moving of the web; and acutting device arranged downstream from said second conveyor for cuttingthe web, wherein said lifting device removes said pressure rollers ofsaid second conveyor from contact with said transport roller just priorto the loop being undone and the web being tightened.
 8. The deviceaccording to claim 7, wherein said continuously driven transport rollerof said second conveyor includes a surface coating having a highcoefficient of friction relative to the web, said high coefficient offriction of the surface coating enabling sudden acceleration of the webwhen said lifting device moves said pressure rollers into contact withthe surface coating of said transport roller.
 9. The device according toclaim 8, wherein the surface coating comprises a rubber-elasticmaterial.
 10. The device according to claim 7, including a thirdconveyor arranged between said clamping device and said cutting deviceand comprising a continuously driven transport roller and pressurerollers, said transport roller of said third conveyor operating at thesame peripheral speed as said transport roller of said second conveyor.11. A device for transverse cutting of a web comprising: a firstconveyor for continuously moving the web along a path of travel at afirst conveying speed; a loop-forming station arranged downstream alongthe path of travel of the web from said first conveyor for storing theweb in a loop during a cutting operation; a clamping device arrangeddownstream from said loop-forming station along the path of travel ofthe web for periodic clamping of the web; a second conveyor including adriven transport roller and pressure rollers provided downstream fromsaid clamping device to drive the web, after being stored by saidloop-forming station, at a second conveying speed which is greater thanthe first speed; a lifting device for removing said pressure rollers ofsaid second conveyor from contact with said transport roller just priorto the web being tightened while the web is clamped; and a cuttingdevice arranged downstream from said second conveyor for cutting theweb, wherein, in operation, said second conveyor is removed from drivingthe web just prior to the web being cyclically clamped by said clampingdevice while said cutting device cuts the web, and after cutting by thecutting device ends, said clamping device is released and said secondconveyor applies a pulling force to the web and accelerates the web tothe second conveying speed.